1. Technical Field of Invention
The present invention relates to a static relay (an electrostatic relay) that opens and closes electrical contacts by driving a movable contact by electrostatic attraction, and a communication device using the relay. More particularly, the present invention relates to a small-size electrostatic microrelay manufactured by using micromachining technology.
2. Background of Invention
As an electrostatic microrelay, one described in the paper xe2x80x9cMicro Machined Relay for High Frequencyxe2x80x9d (Y. Komura, et al.) has previously been known. FIG. 1 is an exploded perspective view showing the structure of this electrostatic microrelay. FIG. 2 is the cross-sectional view schematically showing the structure of the relay. The electrostatic microrelay substantially comprises a stationary substrate 1 and a movable substrate 2. In the stationary substrate 1, two signal lines 5, 6 are formed on a substrate 3. Ends of the signal lines 5, 6 are opposed to each other with a small gap in between, and serve as fixed contacts 5S, 6S, respectively. Fixed electrodes 4A, 4B are disposed on both sides of the signal lines 5, 6. In the movable substrate 2, movable electrodes 9A, 9B are formed, with resilient supporting portions 10A, 10B in between, on both sides of a movable contact 11 formed substantially in the center. Anchors 7A, 7B are provided on the movable electrodes 9A, 9B with resilient bending portions 8A, 8B in between, respectively. The movable substrate 2 is resiliently supported above the stationary substrate 1 by fixing the anchors 7A, 7B onto the stationary substrate 1. The movable electrodes 9A, 9B are opposed to the fixed electrodes 4A, 4B, and the movable contact 11 is opposed so as to straddle the gap between the fixed contacts 5S and 6S.
In this electrostatic microrelay, by applying a voltage between the fixed electrodes 4A, 4B and the movable electrodes 9A, 9B, electrostatic attraction is caused, and by the movable substrate 2 being attracted toward the stationary substrate 1 by the electrostatic attraction, the movable contact 11 makes contact with the fixed contacts 5S, 6S, so that the fixed contacts 5S, 6S are closed to thereby electrically connect the two signal lines 5, 6. Then, by eliminating the electrostatic attraction by removing the voltage, the movable electrodes 9A, 9B are returned to the original shapes by resilience and are separated from the fixed electrodes 4A, 4B, so that the electrical connection between the signal lines 5 and 6 is broken.
An important property of relays is the insertion loss. The insertion loss property shows the degree of signal loss caused between the signal lines when the contacts are closed. Improvement of the insertion loss property means a reduction in the signal loss.
The insertion loss property is determined mainly by the electric resistance of the signal lines and the contact resistance between the contacts. The electric resistance of the signal lines is determined mainly by the width, length and material of the signal lines. The contact resistance between the contacts is determined by the contact force between the fixed contact and the movable contact and the material of the contacts.
To reduce the insertion loss, the above-described electrostatic microrelay operates in the following manner when the contacts are closed: When a voltage is applied between the fixed electrodes 4A, 4B and the movable electrodes 9A, 9B, electrostatic attraction is caused between the fixed electrodes 4A, 4B and the movable electrodes 9A, 9B. Then, the resilient bending portions 8A, 8B bend, so that the movable electrodes 9A, 9B approach the fixed electrodes 4A, 4B and the movable contact 11 is attached to the fixed contacts 5S, 6S. At this time, since the distance between the movable electrodes 9A, 9B and the fixed electrodes 4A, 4B is shorter than the initial one, the movable substrate 2 is attracted by a larger electrostatic attraction, so that the resilient supporting portions 10A, 10B bend. Consequently, the movable contact 11 makes contact with the fixed contacts 5S, 6S with an insulating layer in between. Since the resilient supporting portions 10A, 10B have a larger resilience than the resilient bending portions 8A, 8B, the movable contact 11 is pressed onto the fixed contacts 5S, 6S with a heavy load.
Since the electrostatic microrelay thus has a strong contact force between the contacts, the contact resistance between the contacts is reduced, so that the insertion loss is reduced. Moreover, an excellent insertion loss property is realized by using a low-resistance material such as gold (Au) for the signal lines and the fixed and movable contacts.
Moreover, a mounting configuration of the above-described electrostatic microrelay is such that, as shown in FIG. 3, the electrostatic microrelay is connected to the lead frames 12 by bonding wires 13 so that the fixed electrodes 4A, 4B, the movable electrodes 9A, 9B, the fixed contacts 5S, 6S, the movable contact 11 and the like are made electrically continuous with the lead frames 12, then the electrostatic microrelay is sealed in a molded package.
However, in the electrostatic microrelay with the above-described structure and mounting configuration, since the mounting configuration uses the lead frames 12 and the bonding wires 13, the mounting area of the electrostatic relay in the mounting configuration is large compared to the chip size and the signal line length is large, so that the insertion loss increases to degrade the high-frequency property.
In the above-described electrostatic microrelay, the insertion loss of the relay can further be reduced by suppressing the electric resistance of the signal lines by the shortening signal line length by reducing the size of the electrostatic microrelay.
However, when the size of the electrostatic microrelay is reducing, the areas of the movable and fixed electrodes are also reduced, so that the electrostatic attraction that acts between the electrodes decreases. This decreases the contact force between the contacts. Consequently, the contact resistance between the contacts increases to increase the insertion loss.
As described above, in the electrostatic microrelay of the conventional structure, since there is a tradeoff relationship between the electric resistance of the signal lines and the contact force between the contacts, size reduction of the electrostatic microrelay does not always improve the insertion loss of the electrostatic microrelay.
An object of the present invention is to provide an electrostatic relay capable of reducing the insertion loss irrespective of the size of the relay and the contact resistance between the contacts. Another object is to provide an electrostatic relay capable of reducing the insertion loss without degrading the reliability of the contacts. Still another object is to provide a communications apparatus using the relay.
In an electrostatic relay of the present invention in which a movable electrode of a movable substrate resiliently supported so as to be opposed to a fixed electrode formed on a stationary substrate is driven based on electrostatic attraction caused between the fixed electrode and the movable electrode, and a plurality of fixed contacts provided on the stationary substrate and a movable contact provided on the movable substrate are brought into contact with each other and separated from each other; a sealing portion formed on a third substrate is provided that constitutes a portion that crosses a line connecting the fixed contacts and the movable contact outside a gap between the fixed contacts and the movable contact, and seals at least the fixed contacts and the movable contact by bonding them to the stationary substrate or to the movable substrate, and a through portion in which at least one of the signal lines connecting to the fixed contacts is passed through the stationary substrate from an obverse surface to a reverse surface thereof and is disposed in a position not deteriorating a sealing condition of the sealing portion.
According to the electrostatic relay of the present invention, since the signal lines are passed through the through portion formed so as to pass through the stationary substrate from the obverse surface to the reverse surface thereof, the signal lines provided in the through portion can be directed to the lower surface of the stationary substrate. Consequently, the electrostatic relay is small in size compared to a case where lead frames or the like are used. Moreover, since the signal line length can be shortened, the insertion loss of the electrostatic relay can be reduced, so that an excellent high frequency property can be obtained.
Consequently, according to the electrostatic relay of the present invention, even when the size of the electrostatic relay is the same, the insertion loss can be reduced by reducing the electric resistance of the signal lines by shortening the signal line length. Moreover, according to the electrostatic relay, the electric resistance of the signal lines is suppressed without the contact resistance between the contacts increased, so that the insertion loss property of the electrostatic relay can be improved.
Moreover, according to the electrostatic relay of the present invention, since the fixed contacts and the movable contact are sealed by the third substrate, the atmosphere (kind of gas, degree of vacuum) in the gap between the fixed contacts and the movable contact can be controlled by atmosphere setting at the time of bonding to the stationary substrate, the movable substrate and the like. Further, since the fixed contacts and the movable contact are protected by the sealing, intrusion of foreign objects from outside and deterioration caused by corrosive gases can be prevented, so that reliability and the life of the relay can be improved.
In an embodiment of the present invention, at least one of the signal lines connecting to the fixed contacts is passed through the stationary substrate from the obverse surface to the reverse surface thereof, and an opening, on a movable substrate bonded side, of a through hole through which the signal line is passed is hermetically sealed by bonding it to the movable substrate or to the third substrate through a metal layer formed around the opening. According to this embodiment, since the through hole is used as the through portion where the signal line is provided, the degree of freedom of the position where the through portion is disposed increases. Further, according to this embodiment, since the number of signal lines formed on the stationary substrate is reduced, the areas of the fixed electrode and the movable electrode can be increased without the size of the electrostatic relay increased. Since this increases the electrostatic attraction acting between the fixed electrode and the movable electrode, the contact pressure of the movable contact and the fixed contacts increases, so that the insertion loss of the electrostatic relay can be reduced. Moreover, the driving voltage of the movable substrate can be suppressed by increasing the fixed electrode and the movable electrode in size.
In another embodiment of the present invention, at least one of the signal lines passed through the stationary substrate from the obverse surface to the reverse surface thereof may be formed vertically to the stationary substrate. By forming at least one of the signal lines provided on the stationary substrate vertically to the stationary substrate, the length of the signal line is minimized, so that the effect of improving the insertion loss property can be maximized.
In still another embodiment of the present invention, at least one of wiring conductors provided on the stationary substrate, except for the signal lines connecting to the fixed electrodes being passed through the stationary substrate from the obverse surface to the reverse surface thereof, and an opening on the movable substrate bonded side of a through hole through which the wiring conductor is passed, is hermetically sealed by bonding it to the movable substrate or to the third substrate through a metal layer formed around the opening. According to this embodiment, since the wiring conductor area on the stationary substrate is reduced, the area of the electrostatic relay can be reduced. Moreover, since the fixed contacts and the movable contact are protected by the sealing, intrusion of foreign objects from outside and deterioration caused by corrosive gases can be prevented, so that reliability and the life of the relay can be improved.
In still another embodiment of the present invention, at least one ground line for a high frequency is formed between at least one pair of signal lines or wiring conductors of the signal lines or the wiring conductors formed on the stationary substrate. According to this embodiment, since the capacitive coupling between the signal lines or the wiring conductors can be suppressed by connecting the signal lines or the wiring conductors by the ground line for a high frequency, the isolation property of the electrostatic relay improves.
The isolation property shows the degree of signal leakage caused between the signal lines when the contacts are opened. Improvement of the isolation property indicates reduction in signal leakage.
In an electrostatic relay according to still another embodiment of the present invention, at least one of the signal lines or the wiring conductors is formed in the through hole formed in the stationary substrate, and at least part of the signal line or the wiring conductor is formed only on part of the through hole. According to this embodiment, even when the signal lines or the wiring conductors are opposed to each other, the capacitive coupling between the signal lines or the wiring conductors can be suppressed by partially removing the opposing parts of the signal lines or the wiring conductors, so that the isolation property of the electrostatic relay can be improved.
According to still another embodiment of the present invention, a bump is provided at an end situated on a substrate reverse surface side of at least one of the signal lines or the wiring conductors formed on the stationary substrate. According to this embodiment, since the bump is provided on the reverse surface of the stationary substrate, the electrostatic relay can directly be mounted on the circuit board by the bump. Moreover, since it is unnecessary to form wire pads on the stationary substrate, the element can be reduced in size. In general, a higher packaging density can be realized. Further, since no wire is used, the insertion loss property can be improved.
According to still another embodiment of the present invention, the opening is disposed outside an area on the stationary substrate opposed to the movable electrode or the movable contact. According to this embodiment, since the opening does not overlap the movable electrode or the movable contact, the member for closing the opening does not readily interfere with the movable electrode or the movable contact, so that the degree of freedom of the member for closing the opening increases.
According to still another embodiment of the present invention, the third substrate is bonded to the stationary substrate by a convex portion formed on a side bonded to the stationary substrate. According to this embodiment, since the third substrate has a convex portion for bonding to the stationary substrate, the movable contact and the fixed contacts can be sealed in the concave portion surrounded by the convex portion, so that a simple sealing structure can be realized.
According to still another embodiment of the present invention, at least one of the openings is disposed in a position opposed to the convex portion of the third substrate. According to this embodiment, since the opening can be closed by the convex portion provided on the third substrate, the number of members can be reduced, so that assembly of the electrostatic relay can be facilitated and the cost is reduced.
According to still another embodiment of the present invention, since the through portion is disposed in a peripheral part of the stationary substrate, the through portion can be processed easily. In particular, when the through portion has a concave shape having an opening on a periphery of the stationary substrate, the through portion can be processed more easily. For example, even when the stationary substrate is made of a glass substrate or the like, the through portion can be provided by a method such as sandblasting.
According to still another embodiment of the present invention, since the through portion is formed vertically to a plane of the stationary substrate, the effect of improving the insertion loss property can be maximized.
According to still another embodiment of the present invention, since the third substrate is bonded to the stationary substrate and the through portion is provided on the stationary substrate in a neighborhood outside an area of bonding of the stationary substrate and the third substrate, the sealing structure between the stationary substrate and the third is never deteriorated by the through portion.
According to still another embodiment of the present invention, since at least one of the wiring conductors formed on the stationary substrate is connected to the through portion, not only the signal line length but also the wiring conductor length can be shortened, so that noise resistance increases and the operation of the movable electrode is stabilized.
According to still another embodiment of the present invention, since an electrode film is provided on the reverse surface of the stationary substrate and the reverse surface electrode film is divided into a plurality of areas isolated from each other, by a slit formed on the reverse surface of the stationary substrate, the steps of manufacturing the reverse surface electrode film are simple compared to a case where the reverse surface electrode film is independently formed.
According to still another embodiment of the present invention, since a bump electrically continuous with at least one of the signal lines or the wiring conductors formed on the stationary substrate is provided on the reverse surface of the stationary substrate, the electrostatic relay can be surface-mounted by the bump, so that no lead frame or the like is necessary for mounting.
The stationary substrate and the movable substrate according to still another embodiment of the present invention are made of single-crystal silicon. It is preferable that the stationary substrate and the movable substrate be both made of single-crystal silicon, as all of the steps of manufacturing the electrostatic relay can be almost entirely processed by semiconductor processing steps.
The electrostatic relay of the present invention which is small in insertion loss and excellent in high frequency property is particularly suitable for use in a communications apparatus as a switching element switching transmission/reception signals of an antenna or an internal circuit.
The above-described elements of the present invention may be arbitrarily combined as far as possible.